1. Field of the Invention
The invention relates to an apparatus for optically scanning a surface of an object, which apparatus comprises a radiation source, an objective system for focussing a radiation beam supplied by the radiation source to form a radiation spot on the surface, and a focus error detection system for determining a deviation between the focal plane of the objective system and the surface.
An apparatus of this type is used, for example, when scanning an information plane of an optical record carrier for the purpose of reading recorded information in such plane by means of a read beam or for the purpose of writing information into such plane by means of a radiation beam which is intensity-modulated in conformity with the information to be written. Such an apparatus for scanning the surface of an object may also be used, for example, for measuring the surface height or the profile of the object.